When the trigger is depressed, a throttle wire opens a valve on the carburetor, allowing more fuel to flow in through the jets. If the Ryobi weed eater won't operate at full speed or drops under full load, most likely the fuel or air supply is restricted in the carburetor. Find the source of the loss of air and fuel to get it running properly again.
Clean the Air Filter
The pre-filtration system sits just above the carburetor, and a foam pad cleans all incoming air of minute particles. If the filter pad is clogged or dirty, air will no longer be available to mix with the incoming fuel, and the trimmer will have poor acceleration and won't run properly at full speed. Take the foam pad out of the filter box, and wash it in soapy water with some dish soap; rinse it under clean water, and let it dry thoroughly before reusing it. Replace the foam pad if it can't be washed clean or if it's starting to break apart.
Check the Gas Supply
A Ryobi weed eater uses a mixed fuel of oil and gas. This fuel will start separating inside the tank, fuel lines and carburetor after several days. When the oil and fuel separate and dry, they will leave behind sticky, gummy deposits, which will choke off the fuel supply to the carburetor. Always use freshly mixed gas that's no older than 30 days, and always shake the fuel canister before putting fuel into the Ryobi's gas tank. Dump out any old fuel left in the tank, and rinse out the tank with a little fresh gas, using a brush and rag to clean the walls.
Replace the Pickup
After clearing and washing the tank of any bad gas, inspect the pickup nozzle, or fuel filter, as this screen, if clogged, will stop fuel from entering the carburetor. Pull the old pickup nozzle off the end of the gas line, and check the fuel line. If the fuel lines haven't been replaced in a few years or look dirty or cracked, replace the fuel lines as well, which will ensure the proper amount of gas is reaching the carburetor at all times and will isolate the problem in the carburetor.
Adjust the Carburetor
After swapping out the fuel filter and fuel lines, cleaning the air filter and mixing in fresh Ryobi fuel, adjust the carburetor. Adjusting the carburetor will ensure the mixing screws on the carburetor are opened enough to let a sufficient amount of fuel into the carburetor. Rotate the idle adjusting screw clockwise until the trimmer head starts spinning. Move the screw back 1/8 turn counterclockwise until the head stops spinning. If acceleration problems still persist, take the Ryobi to a professional to clean and service the carburetor's jets, bores and valves.
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